Hydraulics has a history practically as old as civilization itself. Hydraulics, more generally, fluid power, has evolved continuously and been refined countless times into the present day state in which it provides a power and finesse required by the most demanding industrial and mobile applications. Implementations of hydraulic systems are driven by the need for high power density, dynamic performance and maximum flexibility in system architecture. The touch of an operator can control hundreds of horsepower that can be delivered to any location where a pipe can be routed. The positioning tolerances can be held within thousandths of an inch and output force can be continuously varied in real time with a hydraulic system. Hydraulics today is a controlled, flexible muscle that provides power smoothly and precisely to accomplish useful work in millions of unique applications throughout the world.
Most basic systems involve fluid drawn from a reservoir by a pump and forced through a shifted valve into an expandable chamber of a cylinder, which communicates with the work piece, ultimately performing a useful task. After the work is performed, the valve is shifted so the fluid is allowed back to the reservoir. The fluid cycles through this loop again and again. This is a simple on/off operation resulting in only two output force possibilities, zero or maximum. In many industrial and mobile hydraulic applications a dynamic variable force or variable displacement is required. This is accomplished with the use of throttling, a process whereby some of the high-pressure fluid is diverted, depressurized and returned to the reservoir. The use of such a diversion results in an output force at some intermediate point between zero and maximum. If a greater amount of fluid is allowed back to low pressure, the output force is lower. Conversely, if the amount of fluid allowed back to the low pressure portion of the system is less, then the output force is higher. Throttling, while being somewhat inefficient is highly effective.
Another widely implemented form of hydraulics is hydrostatics. A hydrostatic power transmission system consists of a hydraulic pump, a hydraulic motor and an appropriate control. This system can produce a variable speed and torque in either direction. Hydrostatic systems result in an increase in efficiency over the throttling method, but at a high initial expense. An extended control effort is required and response of a hydrostatic system is not as fast as with servo or proportional valves that may be used in a throttling operation.
What is needed in the art is a more efficient hydraulic system for use with mobile equipment.